With Urlacher sidelined for the first time since he missed the final 15 games in 2009, Roach will move into the middle and be replaced by veteran Geno Hayes at the strongside position.

"[Urlacher] is one of the best linebackers in the history of the game," Briggs said. "Plugging Nick Roach in is somewhat comforting because he's played the position and he understands all the calls. It's just kind of about reinforcing his familiarity with playing the 'Mike.'"

Roach has appeared in 76 games with 55 starts in six seasons with the Bears. He made three straight starts at middle linebacker after Urlacher dislocated his wrist in the 2009 season opener. The biggest adjustment he'll face is relaying signals from the sideline to the rest of the defense.

"When you play on the outside you really don't have to get any of the communications," Roach said. "Playing in the middle you have to be the one to initialize all the checks and adjustments."

There was some talk in 2009 that the soft-spoken Roach wasn't loud enough when calling plays. But Briggs isn't worried about his teammate using his "inside voice" Sunday in Minnesota.

"His voice has developed," Briggs said. "I don't know if that's the right word, but he's matured and he sounds louder on the field. Getting the communication is not going to be a problem. Even if the guys don't hear, we've been in this system long enough where we should all understand just by recognizing formations and seeing what teams are in."

With Urlacher unable to participate in the offseason program or preseason games due to a knee injury, Roach took a lot of reps at middle linebacker flanked by Briggs and Hayes.

"That was a big help," Roach said. "Through really the whole offseason up until that first week when Brian came back I was able to go through a lot of the same things."

The Bears' new linebacking trio will be challenged Sunday by Vikings superstar Adrian Peterson, who leads the NFL in rushing with 1,446 yards on 234 carries. What makes that feat even more impressive is that Peterson tore the ACL and MCL in his left knee last Dec. 24.

"He's running stronger since he's come back from his injury than last year, at least me remembering last year when we played the Vikings," Briggs said.

"The guy is a very tough guy to bring down. He's a full head of steam, and once he gets tackled it looks like he's looking for the next time to get the ball. He's pretty relentless, which is great for defensive players. Great players will always raise your level of play."

The Bears' primary objective in every game is to stop the run, though they may be even more focused on that goal without having to account for dynamic receiver Percy Harvin, who was placed on injured reserve Wednesday with an ankle injury.

"The things they were doing with Percy, putting him in the backfield, motioning him out, he could play anywhere on the field," Briggs said. "He's as good a [ballcarrier] as there is in the game. Him not being there, there's a little bit of a relief because he can create some match-up problems."

The Bears (8-4), who are tied with the Packers (8-4) atop the NFC North, no doubt will experience even more relief when Urlacher eventually returns to action.

"It's our job to make sure we get into the playoffs," Briggs said. "Once we get in those playoffs, Brian will be ready and he'll come back and he'll lead us the way he always has."